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Abstract:

The method of the invention comprises imparting to the flaps (6G, 6D) of
said aircraft either a nose-up deflection (αF) corresponding
to the maximum sharpness if the nose-up order is higher than a
predetermined threshold, or a deflection (α0) corresponding to
the minimum drag if the nose-up order is lower than said threshold.

Claims:

1. A method for reducing the takeoff run of an aircraft (AC) provided with
at least one steering joystick (14), with ailerons (6G, 6D) carried by
the wings (2G, 2D) of said aircraft and with mobile aerodynamic rudder
surfaces (7, 9G, 9D), such a takeoff run during which said aircraft (AC)
runs on a takeoff runway (RW) while accelerating and at the end of which
the pilot of said aircraft communicates to said steering joystick (14) a
strongly tilted nose-up takeoff position (βD) so that said
mobile aerodynamic rudder surfaces (7, 9G, 9D) cause said aircraft (AC)
to take off, comprising the steps of:a nose-up tilting threshold
(βs) is determined of said steering joystick (14), lower than
said takeoff position (β0), but sufficiently large to be
representative of the pilot's will to perform the takeoff of said
aircraft; andsaid ailerons (6G, 6D) are controlled so that they take:a
symmetric position (αF) partially deflected downwards
corresponding to a maximum fineness for said aircraft, if the nose-up
tilting (β) of said steering joystick (14) is higher than said
tilting threshold (βs), anda symmetric position (α0)
at least substantially close to that being in continuation of said wings
(2G, 2D) and providing a minimum drag for said ailerons, if the nose-up
tilting of said steering joystick is lower than said tilting threshold
(βs).

2. The method according to claim 1, wherein said nose-up tilting threshold
βS) corresponds at least approximately to one third of the
maximum nose-up stroke (βM) of said steering joystick (14).

3. The method according to claim 1, furthermore establishing a velocity
threshold (VS) for the aircraft running on said takeoff runway (RW)
and in that said ailerons (6G, 6D) take:said symmetric position
(αF) partially deflected downwards corresponding to a maximal
fineness for said aircraft, if the nose-up tilting (β) of said
steering joystick is higher than said tilting threshold (βs) or
if the running velocity (V) of said aircraft is lower than said velocity
threshold (Vs); andsaid symmetric position (α0), at least
substantially close to that being in continuation of said wings and
providing a minimum drag for said ailerons (6G, 6D), if the nose-up
tilting (β) of said steering joystick (14) is lower than said
tilting threshold (βs) and if the running velocity (V) of said
aircraft is higher than said velocity threshold (Vs).

4. The method according to claim 3, wherein said velocity threshold
(Vs) is equal to a few tens of knots.

5. The method according to claim 4, wherein said velocity threshold
(Vs) is at least approximately equal to 40 kts.

6. The method according to claim 3, further comprising: determining
whether the aircraft is on the ground or on flight and in that said
ailerons take:said symmetric position (αF) partially deflected
downwards corresponding to a maximum fineness for the aircraft, if the
nose-up tilting (β) of said steering joystick is higher than said
tilting threshold (βs) or if the running velocity (V) of said
aircraft is lower than said velocity threshold (Vs), or if the
aircraft in on flight; andsaid symmetric position (α0), at
least substantially close to that being in continuation of said wings and
providing a minimum drag for said ailerons, if the nose-up tilting
(β) of said steering joystick is lower than said tilting threshold
(βs) and if the running velocity (V) of said aircraft is higher
than said velocity threshold (Vs) and if the aircraft is on the ground.

7. The method according to claim 6, wherein:there are established:a ground
criterion (CS), being equal to 1 when said aircraft is on flight and
being equal to 0 when said aircraft is on the ground;a velocity criterion
(CV), being equal to 1 when the running velocity (V) of said aircraft is
lower than said velocity threshold (Vs) and being equal to 0 when
said running velocity (V) is higher than said velocity threshold
(Vs); anda steering joystick criterion, being equal to 1 if the
nose-up tilting (β) of said joystick is higher than said tilting
threshold (β3) and being equal to 0 if said nose-up tilting (β)
is lower than said tilting threshold (βs); andeach of the three
criteria (CS, CV, Cβ) is addressed at a respective input of an OR
logic gate or similar (18), having its outlet controlling said ailerons
(6G, 6D):to said symmetric position (αF) partially deflected
downward corresponding to a maximum fineness for the aircraft, if a 1
appears therein; orto said symmetric position (α0) at least
substantially close to that being in continuation of said wings (2G, 2D)
and providing a minimum drag for the ailerons, if a 0 appears therein.

8. An aircraft, implementing the method according to claim 1.

Description:

[0001]The present invention relates to a method for reducing the takeoff
run of an aircraft.

[0002]It is known, that with a view to taking off, the leading edge slats,
the flaps and the ailerons of an aircraft are imparted with a
configuration optimizing the fineness (lift/drag ratio) of the latter,
such that climbing slope becomes maximum. Now, in such a fineness
optimization configuration, said ailerons occupy a position being
partially deflected downwards. As a result, when the aircraft has an
optimized fineness as soon as it has left the ground, the drag of said
aircraft cannot be optimal as long as the latter runs while accelerating
on the ground.

[0003]The present invention aims at overcoming such a drawback.

[0004]To this end, according to the invention, the method for reducing the
takeoff run of an aircraft provided with at least one steering joystick,
with ailerons supported by the wings of said aircraft and with mobile
aerodynamic rudder surfaces, said takeoff run during which said aircraft
runs on a takeoff runway while accelerating and at the end of which the
pilot of said aircraft communicates to said steering joystick a strongly
tilted nose-up takeoff position so that said mobile aerodynamic rudder
surfaces cause said aircraft to take off, is remarkable in that:
[0005]a tilting threshold is determined of said steering joystick being
lower than said takeoff position, but sufficiently large to be
representative of the pilot's will to perform the takeoff of said
aircraft; and [0006]said ailerons are controlled so that they take:
[0007]a symmetric position being partially deflected downwards
corresponding to a maximum fineness for said aircraft, if the nose-up
tilting of said steering joystick is higher than said tilting threshold,
and [0008]a symmetric position being at least substantially close to that
being in continuation of said wings and providing a minimum drag for said
ailerons, if the nose-up tilting of said steering joystick is lower than
said tilting threshold.

[0009]Thus, by means of the present invention, when the aircraft is in a
running phase with a view for a real takeoff, the drag generated by said
ailerons is removed until the pilot controls the takeoff, reducing the
takeoff run. The runway length being necessary to take off could thus be
reduced or, inversely, the aircraft can carry a larger load for a
determined runway length.

[0010]It will be noticed that, although such an aileron drag removal
during most of the running phase occurs to the detriment of the fineness
of the aircraft, no adverse effect results therefrom for the aircraft, as
the fineness is not an important parameter upon running.

[0011]It is known that, generally, said takeoff position of the steering
joystick approximately corresponds to two thirds of the maximum stroke of
said nose-up joystick. More particularly in such a case, a good value for
said tilting threshold could correspond at least approximately to one
third of such a maximum stroke.

[0012]While the operation of all units and devices of the aircraft is
checked, before takeoff and in accordance with a predetermined operation
list (check-list), the pilot could be caused to nose-up deflect said
steering joystick while the aircraft is running at a low velocity. In
order then to prevent the ailerons from switching from one of the
positions to another with no reason, it is then advantageous that the
implementation of the method of the present invention be subject to a
velocity condition. Thus, according to another feature of the present
invention, said ailerons can only take their minimum drag position if the
velocity of the aircraft is higher than a predetermined velocity
threshold, while they take their maximum fineness position if said
velocity of the aircraft is lower than said velocity threshold. Such a
velocity threshold could be of a few tens of kts, for example 40 kts.

[0013]Furthermore, it is known that, should the aircraft be off centred,
the latter could takeoff with a low tilting amplitude of the steering
joystick. Furthermore, for safety reasons, it is important that, on
flight, the aircraft is with its ailerons in a maximum fineness position.
Thus, according to still another feature of the present invention, said
ailerons could only take their minimum drag position if the aircraft is
on the ground, whereas they take their maximum fineness position as soon
as the aircraft leaves the ground.

[0014]As a result from the foregoing, in a preferred embodiment of the
method according to the present invention: [0015]said ailerons are
controlled for taking their minimum drag position when the three
following conditions are simultaneously met: [0016]the aircraft is on
the ground, [0017]and the velocity of the aircraft is higher than said
velocity threshold, [0018]and the tilting of said steering joystick is
lower than said tilting threshold; and [0019]said ailerons are
controlled so as to take their maximum fineness position, when at least
one of the following conditions is met: [0020]the aircraft is on flight,
[0021]or the velocity of the aircraft is lower than said velocity
threshold, [0022]or the tilting of said steering joystick is higher than
said tilting threshold.

[0023]For implementing the present invention, the following actions could
be performed, which consist in: [0024]establishing [0025]a ground
criterion, being equal to 1 when said aircraft is on flight and being
equal to 0 when said aircraft is on the ground; [0026]a velocity
criterion, being equal to 1 when the running velocity of said aircraft is
lower than said velocity threshold and being equal to 0 when said running
velocity is higher than said velocity threshold; and [0027]a steering
joystick criterion, being equal to 1 should the nose-up tilting of said
joystick is higher than said tilting threshold and being equal to 0 if
said nose-up tilting is lower than said tilting threshold; and
[0028]addressing each of the three criteria at a respective input of an
OR logic gate or similar, the outlet of which controls said ailerons:
[0029]to said symmetric position partially deflected downwards
corresponding to a maximum fineness for the aircraft, if a 1 appears
therein; or [0030]to said symmetric position at least substantially close
to that being in continuation of said wings and providing a minimum drag
for the ailerons, if a 0 appears therein.

[0031]Thanks to the previous devices, the method according to the present
invention could be easily implemented in said aircraft.

[0032]This invention thus further relates to an aircraft implementing said
method of this invention.

[0033]The figures of the appended drawing will better explain how this
invention can be implemented. In these Figures, like reference numerals
relate to like components.

[0034]FIG. 1 schematically shows, in top and rear perspective, a jumbo jet
being able to implement the present invention.

[0035]FIG. 2 illustrates, in a schematic side view, the jumbo jet of FIG.
1 during a takeoff phase.

[0037]FIG. 4 illustrates, in three successive phases I, II and III, the
takeoff of the airplane of FIGS. 1 and 2, the phase represented on FIG. 2
corresponding to the phase II of FIG. 4 and phases I and II providing the
takeoff run of said jumbo jet.

[0038]FIG. 5 schematically illustrates the usual position of the ailerons
of said jumbo jet during the phases I to III of FIG. 4.

[0039]FIG. 6 schematically illustrates the position of the ailerons of
said jumbo jet according to the present invention during the quickest
part of the phase I and during the phase II of FIG. 4.

[0040]FIG. 7 is the block diagram of the implementation of the method
according to the present invention.

[0041]On FIGS. 1, 2 and 4, the flaps, the slats, the rudders, the
ailerons, the trimmable horizontal stabilizer, as well as the other
mobile aerodynamic surfaces of the jumbo jet, are shown in a retracted
position for clarity sake of the drawings. It will be easily understand
that during phases I, II and III of FIG. 4, at least some of such
surfaces are, on the contrary, in an extended position, although
represented in a retracted position.

[0042]The jumbo jet AC, schematically shown by FIGS. 1 and 2, has a
longitudinal axis L-L and comprises a fuselage 1 and two symmetric wings
2G and 2D. Said wings carry engines 3 and a plurality of leading edge
slats 4G, 4D and of trailing edge flaps 5G, 5D. Moreover, at the end of
the wings 2G, 2D there are located ailerons 6G and 6D, respectively. As
schematically shown on FIGS. 4 and 5, said ailerons 6G and 6D are
rotationally jointed at the rear of said wings 2G and 2D, respectively,
their downwards rotation stroke α being able to take the maximum
value αM, counted from their position for which they are in
continuation of the corresponding wing 2G or 2D. Such latter position,
being shown on FIG. 6 and for which the stroke α is equal to
0°, is generally that for which the drag generated by said
ailerons 6G and 6D is minimum. However, it could occur that the minimum
drag position of the ailerons 6G and 6D is not exactly the position
corresponding to a equal to 0°, but a proximate position for which
the stroke α is close to 0°, but not exactly nil. Thus,
hereinafter it is considered that the minimum drag position of the
ailerons 6G and 6D corresponds to a value α0 of the stroke
α, such a value α0 being nil or close to zero.

[0043]At the rear of the fuselage 1, the airplane AC comprises a
horizontal stabiliser 7 being able to be set in a tilting condition, as
illustrated by the double arrow 8. At the rear edge of said trimmable
horizontal stabilizer 7, there are jointed rudders 9G, 9D respectively,
able to rotate with relation to said stabilizer 7, as illustrated by the
double arrows 10.

[0044]As known, and as illustrated by FIG. 3, the airplane AC is
controlled in a pitching condition by a tilting steering joystick 14,
available to the pilot, operating said trimmable horizontal stabilizer 7
and said rudders 9G, 9D. In the nose-up direction, the steering joystick
14 generates to this end a nose-up order β addressed to the
actuators (not shown) of said trimmable horizontal stabilizer 7 and of
said rudders 9G, 9D. The maximum nose-up stroke of the steering joystick
14 is referred to as βM, while the nose-up position generally
used by the pilot during a takeoff (phase III of FIG. 4) is referred to
as β0 and corresponds to about 2 βM/3.

[0045]The airplane AC further comprises a main landing gear 11, as well as
a front gear 12.

[0046]FIG. 4 shows three phases I, II and III of the takeoff of said
airplane allowing an illustration of the method according to the present
invention.

[0047]In the phase I, the airplane AC runs on the takeoff runway RW
accelerating with a view to taking off, said main gear 11 being then
compressed by the mass of said airplane AC and by the ground effect.

[0048]During such acceleration phase I, the leading edge slats 4G, 4D and
the trailing edge flaps 5G, 5D are usually extended (not shown), the
trimmable horizontal stabilizer 7 is tilted to be nosed-up by the action
of the pilot on the steering joystick and the rudders 9G, 9D are, for
example, in their position aerodynamically extending said trimmable
horizontal stabilizer 7. In such a usual configuration, the assembly of
said trimmable horizontal stabilizer 7 and of rudders 9G, 9D generates a
nose-up aerodynamic force producing a nose-up pitching moment for the
airplane AC, the configurations of the leading edge slats 4G, 4D and of
the trailing edge flaps 5G, 5D allowing to optimize the fineness
(lift/drag ratio) of the airplane AC.

[0049]Usually, in such an acceleration phase I, the ailerons 6G, 6D are
also used for optimizing such fineness and they are symmetrically
deflected downwards, as illustrated on FIG. 5. To this end, they occupy a
partially position being deflected downwards, defined by a value
αF of the stroke α, lower than the maximum stroke
αM. It will be easily understood that such a position of the
ailerons 6G, 6D partially deflected downwards, although favourable to the
fineness of the airplane AC, actually results in a significant drag,
generated by said ailerons and negatively impacting the performance of
the airplane AC during the phase I.

[0050]Thus, according to the invention, in order to overcome such a
drawback, as soon as, in the phase I, the velocity V of the airplane AC
has exceeded a predetermined velocity threshold Vs (for example,
equal to 40 kt) and the pilot has shown his intention to take off (which
can be materialized by the fact that the tilting β of the nose-up
joystick 14 has exceeded a predetermined threshold βs, for
example, equal to βM/3), the ailerons 6G, 6D are brought back
in their optimum fineness position (α=αF), represented
on FIG. 5, to their minimum drag position (α=α0),
represented by FIG. 6.

[0051]In the takeoff phase II (see also FIG. 2), the pilot of the airplane
AC, via the steering joystick 14, actuates the rudders 9G, 9D and/or the
trimmable horizontal stabilizer 7 (not shown), to cause the assembly of
such rudders 9G, 9D and of such a stabilizer 7 to generate a nose-up
force and a nose-up pitching moment being adapted to impart to the
airplane AC a controlled balance 0C with a value favourable to the
takeoff of the latter. In such a phase II, in order to minimize the drag
generated by the ailerons 6G, 6D, the latter remain in their position
taken in the phase I and represented on FIG. 6.

[0052]With such an aileron position, the airplane AC continues its
acceleration run until the latter takes off and the main gear 11 is fully
off ballast, as shown by the phase III of FIG. 4.

[0053]It will be easily understood that the reduction of the drag provided
by the ailerons 6G, 6D in a minimum drag position (FIG. 6) in the final
part of the phase I and during the phase II, facilitates the takeoff of
the airplane AC and reduces the takeoff run thereof with respect to the
situation where said ailerons 6G, 6D would remain in their position being
partially deflected of FIG. 5.

[0054]It is further to be noticed that, in order to facilitate the
climbing performance of the airplane AC during the takeoff phase III, it
is required to bring back the ailerons 6G, 6D from their minimum drag
deflection position, defined by the value α0 (FIG. 6), to
their downward partial deflection position, defined by the value
αF and corresponding to the optimum fineness (FIG. 5).

[0055]Thus, from the foregoing, it is seen that the minimum drag position
of the ailerons 6G, 6D should only interfere during the phases I and II,
when the airplane is on the ground, that the velocity V thereof is higher
than said threshold Vs and that the steering joystick is deflected
by an angle β lower than the threshold β5.

[0056]On the other hand, as soon as the airplane AC leaves the runway RW
(which is, for example, detected by the main gear 11 being off ballast),
the ailerons 6G, 6D should leave their minimum drag deflection
α0 so as to take their maximum fineness deflection
αF.

[0057]The block diagram on FIG. 7 corresponds to a preferred embodiment of
the present invention. On this FIG. 7, there are shown: [0058]a logic
device 15, receiving from the main landing gear 11 a piece of information
concerning its compression or vacuum relief condition, so that the logic
device 15 can infer therefrom whether the airplane AC is on the ground
(the gear 11 is then compressed) or on flight (the gear 11 is then
extended) and delivers at the outlet thereof a ground criterion CS being
equal to 1 if the airplane is on flight and to 0 if the airplane is on
the ground; [0059]a comparator 16, receiving the running velocity V of
the aircraft AC, knowing the velocity threshold Vs and delivering at
the outlet thereof a velocity criterion CV, having its value equal to 1
if the velocity V is lower than the threshold V, and to 0 if the velocity
V is higher than said threshold Vs; [0060]a comparator 17, receiving
the nose-up order β generated by the steering joystick 14, knowing
the nose-up tilting threshold βS and delivering at the outlet
thereof a joystick criterion Cβ having its value equal to 1 if the
tilting β higher than the threshold βS and to 0 if the
tilting β is lower than the threshold βS; and [0061]an OR
gate (or similar) 18 at all three inputs of which there are respectively
applied the criteria CS, CV, and Cβ and controlling the ailerons 6G,
6D at a symmetric deflection αF if the outlet thereof is at 1
and at the symmetric deflection α0 if the outlet thereof is at
0.

[0062]It is thus easily seen that the minimum drag position α0
(FIG. 6) of the ailerons 6G, 6D is controlled if the three following
conditions are met at the same time: [0063]the airplane AC is on the
ground, and [0064]the running velocity V is higher than the velocity
threshold Vs, and [0065]the steering joystick 14 is nose-up
deflected by an angle β lower than the tilting threshold
βS.

[0066]On the other hand, the ailerons 6G, 6D are controlled at the maximum
fineness position αF, if any of the following conditions is
met: [0067]the airplane AC is on flight, or [0068]the running
velocity V is lower than the velocity threshold Vs, and [0069]the
steering joystick 14 is nose-up deflected by an angle β higher than
the tilting threshold βS.

[0070]It is to be noticed that the logic illustrated by FIG. 7 could be
easily implemented in the on-board calculators of the airplane AC, which,
usually, have available information regarding the nose-up deflection
β of the steering joystick 14, the running velocity V of the
airplane AC and whether the airplane is on the ground or on flight.